Signaling system



Oct. 9, 1928.

1,687,244 R. A. HElSlNG SIGNALING SYSTEM Filed Dec. 22, 1 2

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fay/77 0/747 A fie/isvky. b y My Patented Oct. 9.1928.

x i UNITED STATES 1,687,244 PATENT OFFICE.

RAYMOND A. HEISING, 01E MILLBUItN, NEW JERSEY, A SSIGNOR '10 WESTERNELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION NEWYORK.

SIGNALING SYSTEM.

Application filed December 22, 1820, Serial No. 432,444. RenewedNovember 20, 1924.

This invention relates to signaling systems, and more particularly tosystems employing electron discharge devices as amplifiers andmodulators.

In the well-known application of three-electrode electron dischargedevices as amplifiers, it has been the general practice heretofore tomaintain the grid or impedance controlling element at all times at anegative potential with respect to the cathode or heated filament, ifsuch be used. Likewise, when such a device has been used as a modulatorwherein carrier waves of constant amplitude may be modulated by currentof signaling frequency, 1 the potential of the grid has heretofore beenmaintained negative. In each of these cases the grid has been maintainedat a negative potential in order that none of the electrons emit-ted bythe cathode might pass to the grid and so reduce the otherwise very highinput impedance of the device. Due to this high input impedance, anegligible amount of energy was consumed in the input impedance; but tomaintain this condition, during operation, the amplitude of theimpressed voltage was necessarily limited.

When using electron discharge devices in the manner just described, ithas been customary to connect a very high impedance, for example aresistance of the order of one-half a megohm or more, across the inputterminals of the amplifier or modulator tube and to connect a secondaryof a speech transformer to thishresistance;

According to this invention the grids of thedischarge devices areallowed to become positive,thereby increasing the allowable im-' pressedvoltage amplitude. It has been'found 1 that a maximum of energy can beobtained in the output circuit of the discharge devices with a minimumof distortion of the signaling wave by providing an impedance across thesecondary of the speech transformer and impedance. This impedance maytake the form of a substantially pure resistance.

When large amounts of power are obtained from an electron dischargedevice, such as an' amplifier or a modulator by allowing the peaks ofthe input voltage waves to make the grid positive with respect to thecathode, cur

rent flows from the grid to the cathode as soon as the grid becomespositive. Under this the input circuit of the discharge devices of.approximately the value ofthe' positive grid f the signal cycle when thegrid is positive with respect to the cathode.

condition, the input circuit of the discharge device has a finite,resistance which is often uite low. The in ut impedance of'such a evicesupplymg arge amounts of power may, therefore, be large over most of asignal cycle (say 500,000 ohms for 300 degrees) and fall to a low valueduring the rest of the cycle (say 12,000 ohms for degrees). If thecircuit working into the grid is a high impedance circuit, it willproduce pro er potentials for the 300 degrees of the eye e, but duringthe remaining 60 degrees the impedance of 12,000 ohms will practicallyact as a short circu1t therefor. Distortion of the signal results, dueto the fact that the positive potentials corresponding to the signal,are not faithfully reproduced and impressed upon the grid. To preventsuch distortion, means must be provided to maintain the desired voltageacross the low 12,000 ohms internal impedance as well as across the highinternal impedance of the discharge device during the two parts of thecycle. The input circuit impedance external of the discharge deviceshould, therefore, not be high (500,000 ohms) but should be low (12,000ohms or lower), in

order that it may supply suflicient current to the 'd without excessivepotential drop therem, to maintain on the grid the desired positivepotential in spite of the current which flows. A- circuitthus proortioned will give greater out ut with less distortionthan is the casefor hlghimpedance input circuits. Distortion, due to'current flow in theinternal input circuit path, approaches zero as the.

impedance of the input supply circuit external of the discharge deviceis made to approach zero.- For high grade tone quality voice current, ithas been found sufiicient to make the Impedance of the connected line orand articulation, of repeated or modulated supply circuit below andtothe left of points i 31, 32 of the same order of impedance as theminimum internal impedance between the grid and cathode reached duringthat part of 12,000 ohms) during the cycle. The supply circuit" is thenproportioned accordingl In a radio transmitting system embo ying thisinvention, an electron discharge or vaccircuit of which is connectedtransformer, across the secondary whichmaybe connectedan impedancesubstantially equal to the input impedance of the modulator'tube atsignaling frequencies when the grid is at a positive potential. Thisimpedance, in practice, ma be a'substantially pure resistance of the orer of 12,000 ohms. Resistance values of 500 to 50,000 ohms have beenused.

One embodiment of the invention will now be described in detail inconnection with the accompanying drawing. Fig. 1 of the drawingillustrates one arrangement of a radio signaling system. The dottedlines indicate a transmission line such as an ordinary telephone ortelegraph line, or a connection to a power transmission line which maybe substituted for the antenna. Fig.2 shows a circuit arrangement whichma be substituted for a part of the circuit of ig. 1.

Referring now to Fig. '1, the modulator M supplies energy to an antennaA. A generator of sustained oscillations O, and a speech frequencycircuit S, are adapted to supply energy to the modulator M.

Modulator M, as shown, may comprise a plurality of three electrodethermionic vacuum tu es, having filaments 5, 5, anodes or plates 6, 6and impedance controlling elements or grids 7, 7. The filaments may beheated by a battery 8, while the amount of filament current iscontrolled in the wellknown manner by a variable resistance 9. Energyfor the plate circuit is supplied by a source of unidirectional current10. The plate circuit of the modulator may be coupled to the antenna Athrough a. transformer 11.

The enerator 0 may also comprise a three electro e thermionic vacuumtube of any well-known type. As illustrated, it comprises a'filament 12heated by battery 13 through a controlling resistance 14. The platecircuit is supplied with energy by a unidirectional source 15. The platecircuit and grid circuit are coupled together and to the input circuitof the modulator M through a transformer 16. The frequency of thegenerated oscillations are determined by the tuned circuit comprisingthe primary windings of transformer 16, and the condensers 17 and 18.

The speech frequency circuit S may comprise a microphone 19' adapted toimpress current upon the input circuit of the modulator M throughtransformers21 and 22, thermionic vacuum tube amplifier SA and step-downauto transformer 23. Energy for the microphone may be supplied bybattery serves to maintain the may be of the step-up type, in order totransform the energy of low potential from the microphone circuit toenergy of high potential suitable for impressing upon the input circuitof the speech amplifier SA. A high resistance 24 is also connectedacross theinput of the speech amplifier SA. Battery 25 rid 26 at anegative potential at all times wlth respect to the filament 27. Battery28 supplies energy to the plate circuit of the speech amplifier throughan impedance coil 29, in a well-known man'- ner. By this method ofconnecting a microphone 19 to a speech amplifier SA, a large amount ofenergy of undistorted wave shape is made available at the outputterminals 33, 34 from a limited amount of energy supplied by themicrophone. Suchan arrangement is not new.

According to this invention there is connected across the secondarycircuit of the stepdown antotr'ansformer 23 a resistance 30. Thisresistance is of the order of 12,000 ohms, and its value is so chosenthat it substantially matches the input impedance of the'modulator Mmeasured across the terminals 31, 32 when the grids 7 7 are at apotential positive with respect to the filaments 5, 5. The primary ofthe autotransformer 23 is connected to the output of the speechamplifier SA at the terminals 33, 34.

Condenser 35 serves as apath for oscillations from generator 0 aroundthe transformer 23 and the resistance 30. Condenser 36 provides a highfrequency path around battery 38, which serves to place a certainnegative potential on the grids of the modulator M, or condenser 36 mayact as a storehouse of negative potential, if it is provided with a leakresistance (not shown), due to grid current. The secondary of thetransformer 16 the antenna A. During such operation the potential of thegrids 7, 7 become positive, and as is Well known under thoseconditions,the otherwise almost infinite impedance of the tube is materiallyreduced. In orderto utilize this reduced input impedance eflicient ofenergy-in the; output circuit of the modulator M, this low' ered inputimpedance of the tube has been ly, and to obtain a maximum matched by asubstantially equal external impedance such as the resistance 30. Inthis way it has been found that a larger amount I'Ill i of energy can beobtained in the output circuit former 37 of Fig. 2, with the impedance30 connected across its secondary winding may be connected to the rimaryterminals 33, 34, and secondary termmals 31, 32. The operation is notchan ed by this modification, and thereforen'o further description isnecessary.

-ulation.

To those skilled in the art, other embodi- It is'to be understood thatthis invention is not confined to radio signaling systems, nor in factto signaling systems employing sustained oscillations as carrier waves.It may find application wherever signaling waves are imposed uponamplifiers or modulators, especially where a thermionic vacuum tube isused for the purpose of amplification or modments of this invention willbe apparent. All

such embodiments, as defined by the appended claims, come within. thescope of this invention. l

What-is claimed is: 4

1. A thermionic vacuum tube, an impedance controlling elementand acathode for said tube, an input circuit comprising said im edancecontrolling element and said catho e, a

source of signaling current adapted to im-- press a voltage on saidinput circuit which 7 causes the impedance controlling element to becomepositive with respect to. the cathode during operation, and an impedanceconnected across said input circuit of value substantially the same asthat of the input impedance of said tube when said impedance controllingelement is positive.

2. In a carrier wave signaling system, a modulator, an input circuit forsaid modulator including a cathode and an impedance controlling element,a source of carrier waves and a source of modulating waves associatedwith l said input circuit, said waves having an amplitude of such valueas to cause said impedance controlling element to become positive withrespect to the cathode during operation, and'means tocause the impedanceof said source of modulating waves to" substantially equal the minimumimpedance of said input circuit due to the impedance controlling elementbecoming positive.

grid to "go positive with respect to said cath-' dance connected acrosssaid input circuit 0 3.- In a slgnahng system, a three electrodethermionic vacuum tube, an input circuit comprising the grid andcathodeof said tube, an alternating currentsource connected to said inputcircuit, current from said source having an amplitude of such value asto cause said ode, and an im I value substantially matchmg the'positivegrid andcathode impedance.

4. In a signaling system,

'a three electrodev thermionic vacuum tube, an input circuit comprisingthe grid and cathode of said tube, an alternating current sourceconnected to said input circuit, currentfrom said source having anamplitude of such valueas to cause said grid to go positive with respectto said cathode, and an impedance connected across said input circuit ofvalue not substantially greater than the positive grid to cathodeimpedance. v 5. The method of operatin an electron discharge devicehaving a gri and cathode, which method comprises supplying the gridcircuit of the electron discharge device with alternating currentimpulses of values sufficient to make the potential of said gridpositive with respect to said cathode, and compensating for the lossoccasioned by the consumption of energy in said rid circuit due to thepotential of said gri becoming positive wit respect to its cathode.

6. A supply circuit adapted'to supply electrical impulses, an electrondischarge device connected .to said supply circuit and comprising acathode, an anode, and a control electrode, the magnitude of theimpulses sup.- plied by said supply circuit being suflicien't to makesaid grid positive at times with respect to said cathode, the controlelectrode circuit exterior to said discharge device having an impedanceof the order of the impedance between said control electrode and saidcathode when said control electrode is at a vpositive potential.

A supply circuit adapted to suppl electrical impulses, an electrondischarge evice, means reactively connecting said discharge device tosaid supply circuit, said discharge device having a control electrodeand a cathode, the magnitude of the impulses of said supply circuitbeing suflicient to make the potential of said control electrode attimes positive with respect to said cathode, and

means on the input side of said discharge device for reducing thedistortion ofthe wave pedance substantially matching the impedancevalueof the grid circuit of said second mentioned discharge device underthe condi tion that the grid of said circuit is at a positive potential.

' 9. In a signaling system, an electron discharge device, aninput'circuit for said device I I including a grid and cathode, a sourceof inputener adapted to cause the grid to be come pos tive with respectto the cathode durin operation, and animpedance con-' necte across saidinput circuit of value sub-- I pedance between said grid and saidcathode when said grid is at its greatest positive potential.

11. In combination, a speech frequenc C11- cuit, an electron dischargedevice, a gri and a cathode for said device, a speech frequencytransformer connected between said .speech frequency circuit and saidgrid and cathode, means for causing said grid to become positive withrespect to said cathode, and an impedance connected across the dischargedevice side of said transformer of value substantially equal to theimpedance between said grid and cathode when said grid is at a positivepotential.

12. In combination, a speech frequency circuit, an electron dischargedevice, a grid and a cathode for said device, the internal impedancebetween said grid and cathode varying between limits of the order of12,000 and 500,000 ohms dependent upon the potential of said grid withrespect to said cathode, a

- speech frequency transformer connected between said speech frequencycircuit and said grid and cathode, means for causing said grid to becomepositive with respect to said cathode. and a resistance of the order of12,000 ohms connected across the discharge device side of saidtransformer.

13. In a. signaling system, a source of oscillations, asource ofsignaling current, means to modulate said oscillations in accordancewith said signaling current comprising an electron discharge devicehaving a grid and a cathode, the impressed potential from said source ofsignaling current being of. sufficient magnitude to cause said grid tobecome positive with respect to said cathode, and an impedance connectedacross said source of signaling current of'value substantially equal tothat of the impedance between said grid and cathode when said gridis ata positive potential.

14. In a signaling system, a source of oscillations, a source ofsignaling current, means to modulate said oscillations in accordancewith said signaling current comprising an electron discharge devicehaving a grid and a cathode, means to cause said grid to become positivewith respect to said cathode,

l and an impedance connected to said last mentioned means between saidmeans and said discharge device of Value substantially equal to that ofthe internal impedance between said grid and cathode when said grid isat a positive potential.

15. In a signaling system, an electron discharge device having agrid'and cathode, the internal impedance between said grid and cathodevarying between limits of the order of 12,000 and 500,000 ohms dependentupon the potential of said grid with respect to said cathode, an inputcircuit for said device in- 7 eluding said grid and cathode, a source ofsignaling current, a signaling current amplifier, a step-downtransformer adapted to, receive energy from said amplifier and to supplysaid energy to saidinput circuit, and .0 a resistance of the order of12,000 ohms connected across the low impedance side of said transformer.

16; In an electrical system, an electron discharge device having a gridand a cathode, 5 an input circuit for said device, including said gridand said-cathode, a source of alternating current, an amplifier for saidcurrent, energy translating means connected between said input circuitand said amplifier adapted to receive energy of high potential from theamplifier and to supply energy of a lower' potential to said inputcircuit, said translating means having an effective shunt impedance forsaid input circuit of value substantially the same as that of the inputimspedance of said device when its grid is at a positive potential.

17 In an electrical system, an electron discharge device having a gridand a cathode, an input circuit for said device comprising said grid andcathode, a source of alternating current associated with said inputcircuit, current from said source being of such amplitude. as to causethe potential of the grid to become v alternately positive andnegativewith respect to the cathode, and an impedance connected v across saidinput circuit of value not substantially greater than the grid-cathodeimpedance of said device when the grid is at its max- 'imum positivepotential.

18. In an electrical system, an electron discharge device having a gridand a cathode, an input circuit for said device including said grid andcathode, a source of alternating ourrent, means to connect said sourceof alternating current to said input circuit, whereby the potential ofsaid id with respect to said cathode is rendere positive, and meansassociated with said connecting means to cause the maximum positive andnegative alternating potentials impressed upon said grid to besubstantially numerically equal. f

19. In an electrical system, an electron discharge device having a grid,a cathode, and an anode, an input circuit for said device includingsaid-grid and cathode, an output circuit for said device including saidcathode and anode, a source of alternating current, means to connectsaid source of alternating current Lea-1,24;

to said input circuit; said source being of inwith respect to saidcathode is at times rensaid input rent potential dered positive,andmeans connected across circuittocause the component of current in theoutput circuit corresponding to the impressed alternatin current to havepositive and negative amp 'tudes relatively proportional to thepositiveand negative amplitudes of the impressed alternating current.

20. In an electrical translatin prising an electron dischar e anelectron emitting catho e, an Impedance controlling element andan'anode, the method which comprises impressing alternating .cur-

upon said cathode and imped system comtensity such thatthe potential ofsa1d grid Y device having Y therein, including a high reactance and acon- 25 denser and a resistance in multiple shunted across thefilament-grid circuit.

In witnesswhereof, I hereunto subscribe w my name this 17-thday ofDeeember A.,D., 1920. Y

RAYMOND A. HEISING.

